It is known that molecules which function as immunosuppressive receptors includes CTLA-4 (N. Engl. J. Med., 338(25): 1813-21 (1998)), PD-1 (Proc. Natl. Acad. Sci. USA, 98 (24): 13866-71 (2001)), FcγRIIB (Science, 290(5489): 84-9 (2000)) and the like.
An amino acid sequence of the protein related to the present invention (sometimes referred to as B cell immunoglobulin receptor 1 (BIR1) hereinafter) and a nucleotide sequence of DNA encoding it are reported in WO 99/33873 pamphlet. However, not only functions of the protein related to the present invention are not sufficiently elucidated, uses of antagonists and agonists thereof are not known at all.    [Non-patent Reference 1] N. Engl. J. Med., 338(25): 1813-21 (1998)    [Non-patent Reference 2] Proc. Natl. Acad. Sci. USA, 98(24): 13866-71 (2001)    [Non-patent Reference 3] Science, 290(5489): 84-9 (2000)    [Patent Reference 1] WO 99/33873 pamphlet